Pluto's demotion from a planet to a dwarf isn't the work of
mean-spirited Grinches. It is a necessary part of the same process that
got Pluto discovered in the first place.

September 13, 2006

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As a professional astronomer, I’ve grown accustomed to answering questions about my job: No, astronomy is not the same as astrology; yes, black holes exist; and no, an asteroid will probably not destroy life on the Earth in the foreseeable future. Still, the number and intensity of questions I have been asked surrounding the demotion of Pluto to dwarf planet status has surpassed any astronomy-related news story I’ve experienced before. In one fell swoop, we wicked astronomers seem to have dissed our Solar System’s poor little ninth planet, ruined a classic mnemonic, and forced schools across the globe to revise their science textbooks.

Astronomers are used to a great deal of press coverage per capita. A Google search reveals that there are roughly as many news stories for the 10,000 or so professional astronomers worldwide as there are for the few hundred thousand biologists or chemists. Newspapers’ science sections are often filled with fundamental astronomical discoveries which overturn science textbook explanations. Thus, it is a bit surprising that there has been so much animosity towards calling Pluto a dwarf planet. Youtube eulogies aside, Pluto has not been destroyed. It’s just been recategorized.

Pluto has always been an oddball planet. According to our theories of planet formation, planets close to the Sun (Mercury through Mars) are small and rocky; planets in the outer Solar System (Jupiter through Neptune) are large and gaseous. Pluto, which is small and icy, has never fit in. Talk of its reclassification has been going on for years. The problem is this: If our definition of a ‘planet’ includes Pluto, then there are several recently discovered Pluto-like objects in our Solar System which should also be allowed to join the planetary club. But if we wish to restrict club membership–and not admit every new ball of ice or rock found in the Solar System–then Pluto has to go.

While the media has explained the reclassification of Pluto with varying degrees of accuracy, many have noticed the internal disagreement within the astronomical community. Take for example a rare showing of media bipartisanship. Both the New York Times [5] and the Colbert Report [6] called astronomers out on our John Kerry-like moment where we voted to keep Pluto as a planet less than a week before voting against it at the recent General Assembly of the International Astronomical Union (IAU).

And the flip-flopping may not yet be over. Protesters at New Mexico State University where Pluto’s discoverer, the late Clyde Tombaugh was a professor emeritus, argued that because only about ten percent of astronomers voted for the change, the electoral result is unrepresentative. The difficulty with this argument is that astronomy is a diverse field with many different areas of specialization. The majority of astronomers don’t work on planets. It would be like questioning the results of a Republican primary because the Democrats failed to vote.

And this is probably the point for full disclosure. In my research I study galaxies at distances which make Pluto seem closer than your next-door neighbor. While there were galaxy-related talks and sessions at the IAU meeting, I did not attend nor did I vote on various resolutions including those related to the renaming of Pluto.

Whatever its definition, Pluto remains high on my list of admirable discoveries. Unlike most “official” planets which are visible from earth with the naked eye, Pluto’s discovery represents the fruit of a carefully planned scientific experiment. In 1930, Clyde Tombaugh found Pluto by comparing pairs of photographic plates taken at the Lowell Observatory, searching for faint objects moving against the constant background of stars. The search was tedious and not particularly romantic, but well worth the effort. Modernized versions of this same technique have uncovered a wealth of objects in the outer Solar System including a few Pluto-like objects.

So, why change Pluto’s status now? While I doubt Pluto cares very much about its “demotion,” clearly humans do. The answer is science. New discoveries highlighted a flaw in our nomenclature that needed to be corrected. And while we do not learn anything new by calling Pluto a ‘dwarf planet’, the discussions around its renaming may lead to new ideas about how planets form. Pluto’s downfall isn’t the work of mean-spirited Grinches, it is a necessary part of the same process that got Pluto discovered in the first place.

Ironically, there was another vote taken at the same IAU meeting last month: adoption of new set of guidelines for communicating astronomy to the public. Regardless of Pluto’s status, astronomers will continue to study Pluto as well as ways to better communicate this research to the public. In the meantime, repeat after me: “Pluto is big enough, it’s round enough, and doggone it, people like it.”

Marla GehaMarla Geha is an astronomer and Hubble Postdoctoral Fellow at
the Carnegie Observatories in Pasadena, California.